Discussion in 'General Technical Questions and Answers' started by G4ALA, Jul 24, 2008.
From amateur radio regulations, FCC part 97.3, where many definitions are given:
The PEP is the summation of instantanious ((peak to peak voltage) squared) divided by the load Zo through the through 360 degrees of the modulating signal. This summation product will varie with the shape factor (distortion ) of the modulating signal and the RF carrier. Now I forgot everything I ever knew about calculas 30 years ago. So I generalize,, With a two tone modulating signal, I use Avg power X 1.57. The bird wattmeter presents Avg power.
Pep is like vigor...except more...um...PEPPY!
Here is a little more information to clarify/muddy the waters.
Having obtained an MFJ antenna tuner with a slightly burned our SWR meter some years ago, I repaired it and re-calibrated it using dummy loads to set various SWR levels and a calibrated oscilloscope to measure the peak voltages. I set the power reading to read RMS power.
Later comparison with another MFJ meter, which had the factory settings intact, showed that the two sets of readings were the same.
In other words, when my MFJ meter is on "peak", the peak indicated is the "peak RMS" ans opposed to "peak instantaneous".
Hence my question.
You can calibrate any meter to read either average, or PEP- but the caveat is that it can only be used to measure steady signals, like a two-tone test for ssb.
A simple test to see if your instrument is really peak reading, is to send a single dit. A true peak reading instrument will read full power, any sort of average reading instrument will read a great deal less, if at all.
I didn't want to do this but I'm including a link to answer your question and more. Read or scan read the article, their graphics are quite good but the theory can be a little intense at times.
Your measurement sounds correct for a single tone (CW) signal, the peak and average power are the same, the ratio is 1:1.
I'm gonna put some popcorn in the microwave...
Peak RMS or peak average power would be correct. Your meters are calibrated properly.
::I doubt you can measure RMS power. That takes extremely complex and sophisticated analyzing and processing circuitry, or the ability to dump all the power into a passive (resistive) load that dissipates all power applied, and then measure RMS power as heat rise in that load. There's no other way to measure RMS power that I know of.
You're measuring average power.
There's a difference, as soon as you introduce any distortion. Measuring power by thermal rise, it will be correct if the applied signal is a sine wave, or not. It can be a pulse, a square wave, triangular wave or anything else, RMS will still be RMS.